With reference to FIG. 6, a conventional flexible substrate 10 includes a base layer 11 and a trace layer 12, wherein the base layer 11 comprises a first surface 11a and a second surface 11b, the trace layer 12 is disposed on the first surface 11a of the base layer 11, and an identifying code 13 is formed on the second surface 11b of the base layer 11 by means of printing for manual interpretation or photography interpretation. However, owing to the identifying code 13 formed on the second surface 11b of the base layer 11, when one is about to interpret the identifying code 13, the flexible substrate 10 has to be reversed and thereafter proceeds interpretation via the second surface 11b of the base layer 11. Therefore, the interpretation time has increased.
Besides, the position of the identifying code 13 formed on the second surface 11b of the base layer 11 for each manufacturer is different, and the handwriting of the identifying code 13 is tiny. For mentioned reasons, the identifying code 13 is difficult to be distinguished.